The present invention relates to an apparatus for fluidizing a particulate material in a conveying gas for transport and distribution, and, more particularly, to such an apparatus adapted for feeding particulate material in a conveying gas to a fluidized bed furnace.
In a typical present day fluidized bed furnace, particulate fuel, such as coal having a top size ranging from about 3.0 to about 6.5 mm, is typically fed to and combusted within a fluidized bed of similar sized particulate material at relatively low temperatures of 760 C. to 925 C. If the fuel being burned contains sulfur, it is customary that the particulate material making up the bed be comprised of a sulfur absorbent, most commonly limestone, in addition to the particulate fuel. Fluidizing air, which also serves as combustion air, is supplied to the fluidized bed from an air plenum located beneath the bed support plate. The fluidizing air passes upwardly from the air plenum into the fluidized bed through a plurality of holes in the bed support plate at a flow rate sufficiently high to fluidize the particulate material within the fluidized bed.
A number of different approaches have been suggested for feeding particulate material to the bed, including overbed feed systems and underbed feed systems. One particular underbed feed system suitable for feeding particulate material to a fluidized bed is disclosed in U.S. Pat. No. 4,356,779. As disclosed therein, a fuel feeder is disposed beneath the fluidized bed combustor for entraining fuel in air and then feeding that fuel upwardly into the combustor. The feeder housing defines a chamber which is divided into upper and lower sections by a horizontally disposed perforated distributor plate. The particulate fuel to be supplied to the fluidized bed is fed into the upper chamber above the perforated distributor plate while conveying air is supplied to the lower chamber beneath the perforated distributor plate. The air supplied to the lower chamber passes upwardly through the perforated distributor plate to fluidize and entrain the particulate coal in the upper region of the chamber. The entrained coal is then carried upwardly from the chamber to the fluidized bed boiler through transport lines which open to the fluidizing chamber through the roof of the feeder.
One problem encountered in using such a fluidizing feeder to convey particulate coal to a furnace through a plurality of transport lines lies in controlling not only the overall output of particulate material from the feeder, but also in selectively distributing that output as desired through the various transport lines leading from the feeder. In the feeder disclosed in U.S. Pat. No. 4,356,779, the particulate material to be conveyed must first be entrained in the conveying gas in a venturi section disposed intermediate the transport lines and the fluidizing chamber. Control of the overall output of such a feeder is limited by the control possible over the entrainment velocity attainable by the conveying gas. Additionally, the output of particulate material from the disclosed feeder is evenly distributed amongst the various transport lines leading from the feeder. No provision is made to permit an uneven or selective distribution of the output.
Accordingly, it is an object of the present invention to provide an apparatus for fluidizing a particulate material in a conveying gas wherein the output of particulate material is controllable as a function of the input of particulate material to the feeder.
Further, it is an object of the present invention to provide an apparatus for fluidizing a particulate material in a conveying gas wherein the output of particulate material is selectively distributable amongst a plurality of transport lines leading from the feed apparatus.